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I know that spray polyurethane foam is difficult to remove and separate from other building materials. Also, dust particules containing toxins can be released when applying or removing it. What is a greener and healthier alternative?

I know for insulation purposes there are good alternatives such as cotton/denim insulation, cellulose insulation or mineral wool, but I'm actually looking for a material that can be sprayed or glued on and is fairly strong when hardened. Any insulation value is a bonus, but not strictly required. Does something like this exist?

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  • Your 2nd to last sentence seems to imply you aren't concerned about insulation. What exactly is the purpose if not insulation? There's many fillers like wood, mud, bricks, gravel, sand, concrete. It all depends on what you are trying to do.
    – Jeff-Inventor ChromeOS
    Aug 14 '14 at 6:10
  • @Jeff-InventorChromeOS I'm trying to close a small hole in my concrete floor. The hole is over a small inaccessible crawlspace. I've been told that the best way to fix it is to first preliminary close it by either nailing a piece of wood at the bottom of the hole (top of the crawlspace), or apply polyurethane foam. Once the wood or foam is in place I can pour cement over it. I was unsuccessful applying the wood because the available space is too small.
    – THelper ♦
    Aug 14 '14 at 7:18
  • I've a similar problem to that, actually. One area of my basement floor is failing but the crawlspace is too narrow to fix it from below. I'm probably going to get a contractor. If he suggests something, I'll post it.
    – Jeff-Inventor ChromeOS
    Aug 14 '14 at 7:30
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A trick I've seen used for repairing drywall holes:

Cut a piece of wood that is roughly elliptical with the narrow dimension being just under the widest dimension of the hole.

Drill two holes in the center and string a loop of cord through it.

Check that the wood will go through the hole.

Apply a bead of constrution adhesive to the wood, then re-insert, and use the string to pull it against the back side of the hole.

Place a bar across the hole, and tie the string to the bar.

You can put a pencil through the two strands, and winch it tight.

For walls, you'd use scraps of drywall. For floors, scraps of OSB, plywood, paneling work..

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Apparantly Icynene is more environmentally friendly than traditional spray polyurethane foam, but it is more expensive and needs to be applied by professionals. Icynene still is a polyurethane foam, but it is PBDE free and isn't as unhealthy in use and removal. More info on the different types of Icynene also here.

Another alternative is soy-based spray foam, but critics say that those aren't very well tested yet and contain very little soy (15%) and still much polyurethane.

I ended up using paper mache myself, made from old newspapers and wallpaper glue. I used it to close a small hole in our concrete floor provisionally. I created a layer of approximately 2cm (about 0.8 inches) and after the paper dried it was fairly strong. Then I added a thin layer of concrete on top of it (only thin because I wasn't sure about the strength of the paper layer). Once the thin concrete layer dried I added more concrete and closed the gap entirely.

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